dcsimg Bracing offshore wind farms for extreme conditions - Ramboll Group
    
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Wind farms in Basse-Normandie
Project data
Client: Éolien Maritime France – EMF

Services we provided
Wind energy
Offshore wind

The team
Santiago Paredes Pinzon
Malene Seidahl Beck

Bracing offshore wind farms for extreme conditions

Basse-Normandie, France ¤

Designing offshore wind farms that can resist strong currents, heavy wind, powerful waves and rapid erosion is no walk in the park. Ramboll is currently shaping two new wind parks with monopile foundations off the French coast that can withstand the harsh conditions and provide renewable and cleaner electricity. 

Picture 80 wind turbines at sea. Piling up next to each other, they accumulate a big, isolated family. But they are not completely alone. Currents, wind, waves and erosion pose a constant threat, making heavy weather their worst enemy.

Ramboll is designing two new wind farms off the French coast where one of the main concerns is the ability of turbines to resist external shocks and stresses from extreme weather.    

- We’re conducting several studies within the scope of work for the basic design of these two farms. For instance, we’re examining how the design can protect wind turbines from the force of big waves breaking on the foundations, explains Project Manager Malene Seidahl Beck, before she provides a less likely, yet relevant scenario:

- It doesn’t happen very often, but if the wave meets the monopile foundation with a specific combination of wave height and wave period during a storm, it can cause the wave to run vertically up the monopile and hit the external work platform with a high upwards force. These worst-case scenarios also need to be taken into our design considerations.

Besides the wave methodology and forces, the design team is also looking at defending the seabed against erosion by putting different layers of stones around the foundation that are too heavy for waves and currents to move. Not a simple task, considering the powerful environmental effects and water depths down to 31m.

155 wind turbines at sea

The two new wind farms, Courseulles-sur-Mer and Saint Nazaire, are located off the northwestern coast in the Basse-Normandie region and the western coastline respectively. Together, the towering constructions make out two thirds of a 1.5 GW wind farm project secured by EMF within the tender launched by the French government in 2011. The remaining third, the Fécamp wind farm, is located off the northwestern coastline, east of the Courseulles farm, but is not part of Ramboll’s scope of work.

The Courseulles wind farm (COU) is based on 75 Alstom 6MW wind turbines and has a planned capacity of 450 MW, whereas the Saint Nazaire project (SNA) is based on 80 Alstom 6MW wind turbines, with a slightly larger capacity of 480 MW.

- The purpose of the wind farms is to convert wind energy into electricity and to benefit the consumers in France with renewable, cleaner electricity and to reduce CO2 emissions, explains Malene Seidahl Beck.

A network of cables transports the electricity to an offshore transformer station, which converts the generated electricity into 220 KV alternating electric current. The export cables then transport the electricity to the transformer station on shore, where the electricity is converted into high-voltage current of 380 KV, before it is distributed into the national grid and finally to the end-users.

The wind farms both have a design life of 25 years after which the wind farms and everything placed on the seabed will be decommissioned.

Malene Seidahl Beck
Malene Seidahl Beck
Project Manager, Offshore Wind
T+45 51615566
Emas@ramboll.com